The present invention relates to inlet guide vanes for centrifugal compressors and more specifically relates to an inlet guide vane assembly for a compressor system which selectively controls the flow angle of fluid passing through a centrifugal compressor so as to maximize the operating efficiency of the compressor. In highly preferred embodiments, the present invention relates to an inlet guide vane assembly for a cooling system which selectively controls the flow angle of a refrigerant or cooling fluid passing through a centrifugal compressor so as to maximize the operating efficiency of the compressor.
In response to the worldwide concern about depletion of the ozone layer, and in order to comply with federal, state and local laws, many organizations, including various organizations within the United States government, are retrofitting cooling systems so that the systems may operate using non-ozone-depleting refrigerants. These retrofitted systems typically use the non-ozone-depleting refrigerants designated R124 and E134, rather than the ozone depleting refrigerant designated R114. However, when using the R124 and E134 non-ozone-depleting refrigerants, the volume flow rates required to produce the desired level of cooling are substantially less than those required when using the R114 ozone-depleting refrigerant. Therefore, these centrifugal compressor systems must be redesigned in order to operate more efficiently at relatively lower flow rates.
The performance of a compressor system is typically modified by changing the operating parameters of the system. U.S. Pat. No. 4,503,684 discloses a control system used in conjunction with a variable width diffuser for monitoring the lift and the load placed on the compressor and adjusting the movable wall position to maintain the system at or close to optimum operating conditions. The load is determined by measuring the current flow through the compressor motor while the lift is determined by comparing the temperature of the water leaving the evaporator and the condenser of the refrigeration system.
U.S. Pat. No. 4,616,483 discloses a refrigeration system that utilizes a motor driven centrifugal compressor having a moveable wall positioned in the diffuser that permits the width of the diffuser passage to be varied to meet changing load conditions within a desired operating range. The percent of full load current drawn by the compressor motor is continuously monitored, thereby providing an indication of the percent of full load capacity at which the compressor is operating. The diffuser wall position is changed in response to changes in measured compressor motor current to locate the wall at an optimum operating position for the measured load.
The mass flow rate of the refrigerant delivered to the impeller of a centrifugal compressor is generally varied in response to the changing demands placed upon the system. The mass flow rate of the refrigerant may be modified by adjusting the position of the inlet guide vanes located upstream from the impeller. U.S. Pat. No. 4,969,798 discloses a diffuser for a centrifugal compressor which enables the compressor to be operated with high efficiency over a wide range of flow rates. The centrifugal compressor includes an impeller rotatably mounted on a downstream side of a suction casing and a plurality of radial stator blades arranged tangentially with respect to the impeller. The kinetic energy of the fluid discharged by rotation of the impeller is converted into pressure energy. The diffuser includes auxiliary blades provided between the impeller and the stator blades. Each auxiliary blade has a chord length shorter than that of the stator blades and is slidable in an axial direction of the impeller. In order to improve operational efficiency, the compressor may include inlet guide vanes and an inlet guide vane actuator for selectively controlling the position of the inlet guide vanes so as to improve impeller capacity by generating whirl to the suction casing.
Despite the above efforts for improving the operation of a centrifugal compressor, there remains a need for an inlet guide vane assembly which maximizes the operating efficiency of centrifugal compressors at different operating rates.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.